Winging It! 36v system for Park Model RV.

[jgriffin]

Hey everyone. This is my first attempt at a Solar Power System (Hence the 36v!). I’m too stubborn to give up on it, so I’m going to be updating my progress as I go.

Equipment purchase so far:

8 - A123 used Hybrid bus modules. 96 LifePo4 Cells, 12s8p. Originally rated just shy of 750 wh, but expecting 450-500 usable. If more, great! Will run between 3.0 and 3.55v.

12s Smart BMS with low voltage cutoff.

3kw Reliable 36v Inverter (Very limited options!).

Renogy Rover 60 amp mppt charge controller.

21 - Silfab 265 watt mono B-Grade solar panels. Because of my remote location, it’s best just get a pallet and sell off what I don’t need. I’m thinking a 3s3p configuration should work, each panel open voltage is 38v, and just over 9 amp. 4s would put me at 152v open voltage, better safe than sorry.

Cheap A/C variable rate charger. Some various breakers, gauges, Bluetooth adapter for BMS are on the way. Anyone shopping in Canada, look out for hidden FedEx fees getting stuff from the US! Ouch.

We typically use IBC cages for firewood, and the plastic inside gets tossed. I fashioned out a door quickly and stuffed an entertainment rack destined for the landfill into it. This was going to be my initial place for batteries and equipment. My father come along, shook his head, and convinced me to use a metal shipping crate his tarp shed arrived in. Much better idea. I’ll rigid foam insulate an area big enough for the equipment, put up some plywood, attach things properly.

We’re on an island in Southern New Brunswick, Canada. It’s actually geographically closer to Maine. This is for my in-laws who have been having some health issues lately, so I’m trying to make things as easy as possible for them.

The RV was on a nearby property for years, but this is the first year for this lot in particular. I’m hoping to figure out a gravity fed IBC system for water, want to avoid using a pump if possible.

Any and all feedback is greatly appreciated! I’d like to thank Will for sharing his wealth of information to us all. I’m actually a lineman who works on the grid daily, so this is a new and exciting challenge!

 

[snoobler]

Welcome to the forum.

Gravity feed is easy unless you want water pressure.

Convert foot of head to psi - Conversion of Measurement Units

Do a quick conversion: 1 feet of head = 0.43341651888775 pounds/square inch using the online calculator for metric conversions.

www.convertunits.com

Need just over 100ft of head to develop 45psi.

 

[jgriffin]

Pump it is!

I’ve seen situations with a tote stacked onto another tote providing adequate pressure, then noticed the bottom tote looked extremely bloated! I didn’t want to get into building too robust of a structure to support that much weight either.

I do have a steep hillside at the back of the property, but a dug well with pump is looking pretty good vs running that much pipe. There is an abandoned dug well on our right of way to the property I wanted to investigate. I don’t know where the neighbours septic is to see if it’s far enough away.

Then again, I could probably use the trailers existing setup and just beef up the pump size. Use the ibc tote to keep the on board tank filled, forego the city water connection entirely. I liked having that system run independently as a backup, but makes sense to utilize it if/until we dig a well.

 

[jgriffin]

Update:

Haven't had much opportunity to work on this, but I did manage to get 1/2 of my battery assembled, and the other 4 modules have arrived that I'll likely just set on top of the existing to save space. Had to swap out my Renogy 60A Charge Controller after a mixup on their end (they completely come good for it though), so upped my budget dramatically.....going with a Midnite Solar Classic 150. I figured if I'm not keeping an eye on this consistently, and with spotty wifi coverage I can't rely on an internet connection to be stable enough, I best get a damn nice Charge Controller. In my cold climate, morning spikes were a concern as well, so the Hyper VOC really appealed to me. I want to make this as easy as possible for my in-laws, they've had some major health issues lately and I don't want them to worry about electronics they don't quite understand. I just want them to enjoy the property ultimately.

Lumber prices have skyrocketed here, much like everywhere else. A single 2x6x12' Kiln Dried was about 26$ CAD! So i'm feeling better about my repurposed Metal Container vs baby barn. I do have some cedar on the property I can mill out, but that's not going to happen anytime soon.

I'm going to line the inside of the metal container with 1" rigid foam insulation, and later work out an option for some vents/fans for the summer. I"d like to be able to block off the vents in the Winter, so a combination of battery heating pads and insulated space will hopefully keep things warm enough to charge smoothly in the winter. I do have the option to not use this system in the winter as well, pack it all up and move it to my home to keep warm in the garage, and use for emergency backup.

Well, my wife can while i'm out fixing the grid.

I'll post a few pictures of my progress. I need another mount for the remaining 3 panels. And I need to straighten the panels on the repurposed pop up trailer frame as well.

Question is....did I get my fusing right? Midnite Solar MNEDC100 Breaker between Panels and Charge Controller, 100A DC breaker between Charge Controller and Battery Source side, then 150A "up to 48v" breaker between Battery Load side and Inverter. I was a little torn on sizing the pv side, I think i'm ok with foregoing the 25% of max amperage. I'm going to be open circuit about 30A total, just that the Charge Controller is sized just under 100a. Think 95'ish. I'm going to run it by the shop when I pick up my Charge Controller tomorrow, see what they think I should have instead.

 

[jgriffin]

Solar array (need to mount 3 more somehow), and battery with 4 of 8 modules together.

 

[jgriffin]

I finished the bus bars and wiring. Bus work is basically the same on the other side. Plenty of chances to wire up accessories, and large terminals to bolt the Charge Controller and Inverter. With another pallet on top, I can build onto this the very same, just keep wiring each the same. Next time I would go with a different configuration, I had imagined a cleaner look at the end, but something I can keep working on.
I also don’t like how small the screws are to each positive and negative post on each module. A copper bus bar with packs stacked vertically would no doubt be easier.

 

[jgriffin]

It's alive!

Just looking for some input on my BMS settings. I currently have 8 36v 12s8p LifePo4 modules. They use the A123 They are well used, haven't actually done full capacity tests yet to see what they'll still do.

New, they're rated for 736 Watt Hours, I'd have to guess they're around the 500 range, not entirely sure. Should I use the full 736 watt hours to find total capacity for battery charging figures? These values only are a point of reference, they don't change the characteristics of the BMS to my knowledge. I figured if I converted to the whole Design Cap value to mAH, then put cycle cap at 80%, that'd get me close so I could look at the bms and see % of discharge whenever.

What's more important I suppose, is that I have my Basic Parameters set properly. On my Midnite Solar Classic 150 Charge Controller, I have high cell cut off at 3.55v per cell. If something were to go amiss with that, then the BMS should open at 3.6v per cell. On the CC I have 41.5v for absorb, 41.0 Float, i'll bump it up a bit once I get a first few cycles on this to see how it's going to react.

Where I was leaving the site and not keeping too close of an eye on it, I actually limited the Output Amperage on the CC to 15a. That still let me bring in about 550 watt while it was left. I decided to go 3S2P for now, and it's actually done better than I expected. Seen 1200 watt while I was on site, panels aren't even pointed correct and angle is way off! I didn't feel too great about leaving it unattended with 30A on it's maiden voyage.

Either way, still winging it. Any input as to what I should be doing is greatly appreciated. I need to work on my array, we get high winds and I need to permanently mount them soon. I'll take some pics of the build in its entirety soon, That too needs tidying up a bit.

 

[jgriffin]

This Charge Controller is great! Gives me peace of mind.